New bi-nuclear and multi-nuclear α-diimine/nickel catalysts for ethylene polymerization

Abstract

Bi-nickel-centre catalysts {[2,6-diisopropyl-C 6H 3 N C(CH 3) (CH 3)C N 3,5-di-R C 6H 2 CH 2 3′,5′-di-R C 6H 2 N C(CH 3) (CH 3)C N 2,6-diisopropyl-C 6H 3][NiCl 2] 2; R, CH(CH 3) 2, CH 2CH 3, CH 3} were prepared by Schiff-base condensation of 2,3-butanedione with 2,6-diisopropylaniline and substituted bis-aniline, and subsequent metathesis reaction with (DME)NiCl 2. Multi-nickel-centre catalysts { [( N C(CH 3) (CH 3)C N 3,5-di-R C 6H 2 CH 2 3′,5′-di-R C 6H 2 ) NiCl 2] n ; R, CH(CH 3) 2, n = 4.0; R, CH 2CH 3, n = 4.0; R, CH 3, n = 2.5} were prepared by Schiff-base condensation of 2,3-butanedione with substituted bis-aniline, and subsequent metathesis reaction with (DME)NiCl 2. Comparing with mono-nickel-centre catalysts, the new catalysts have much bigger molecules, particularly the distance between every two active centres was controlled for bi-nickel-centre catalysts, and the distances among several active centres were controlled for multi-nickel-centre catalysts, resulting in the micro chemical environment of nickel centre being regulated. The catalytic evaluation clearly showed that this structural regulation had significant influence on catalytic activity. When the substitute was isopropyl or ethyl, the new catalysts demonstrated much higher catalytic activity than the corresponding mono-nickel-centre catalysts; but when the substitute was methyl, the new catalysts demonstrated lower catalytic activity than the corresponding mono-nickel-centre catalysts. The most efficient new catalyst was multi-nickel-centre catalyst with ethyl as substitute, which catalytic activity was high up to 3220 gPE/(gNi h) at 25 °C with Al(MAO)/Ni ratio at 500.